The invention relates to the field of guided airborne payloads and geolocation methods used by airborne vehicles. More particularly, the present invention relates to reference beacon geolocation methods by airborne beacon reference vehicles cooperating with airborne target-geolocating unmanned vehicles.
Stationary beacons, such as stars or ground-based reflectors, optical beams, and radar transponders, are commonly used as geolocation references. Examples of stationary-beacon geolocating systems includes split-field and star reference systems. Split-field reference attitude systems superimpose star images on photographs of ground objects. With knowledge of the latitude and longitude of the sensor platform and the time of day, the coordinates of objects in the photograph can be determined relative to star images on the film. Star-reference attitude systems perform a similar function. Portable radar transponders can be used as references as well for geolocating a target. In one application, the transponders are deployed by ground troops to designate the position of a nearby ground target for bomber aircraft. Surveyed latitude and longitude offsets from a target location relative to the beacon location appear as electronic blips on aircraft radar displays to indicate the target location to the bomber pilot. In other applications, flashlight infrared beacons allow individual soldiers to indicate their locations to helicopter pilots who can see the beacons with their night vision goggles. Target offsets relative to the soldiers"" positions are radioed to the pilots for close-air-support missions.
To avoid risk to manned-piloted missions, unmanned vehicles are becoming widely used for surveillance and targeting of military, terrorist, and civilian targets. Technology trends include fire and forget smart munitions with communications networking and information sharing with unmanned vehicles both as sensor platforms and as weapon platforms using smaller bombs for striking multiple targets while reducing collateral damage and reducing logistics tails. More capable unmanned vehicles are to be widely deployed in future conflicts in aid of advanced tightly integrated command and control functions through the use of advanced communications technologies. An unmanned vehicle can loiter in a search area and perform real time surveillance so that operators at remote sites can designate targets, release stand-off smart bombs or missiles, and then acquire damage assessment in real time. Unmanned vehicles can be adapted for dropping large numbers of low-cost precision-guided miniature bombs that separately target respective targets.
Targeting sensors using infrared sensing and mounted on unmanned vehicles have about a one foot resolution from about 5000 feet altitude but suffer from geolocation errors that may be as high as 100 feet due to poor altitude determinations. Bombers and satellites use star trackers to obtain precise altitude determinations. Star trackers could be adapted for low altitude unmanned vehicular operations, but star trackers are expensive and operationally complex, and unsuitable for cloudy environs. Stars for star tracking may not be visible from aircraft flying at low altitudes below the clouds. As such, star tracking may not always be suitable as a means for attitude determination for low altitude unmanned vehicles. Though widely employed, stationary beacons are not often suitable for calibrating the boresight pointing angles of aircraft-based sensors. Also, it may not always be feasible at times to place ground beacons close to targets of interest.
Militarily, present trends are toward smaller and smarter weapons to precisely strike targets, such as trucks, fuel depots, power generators, missile sites, and terrain sites for obstructing moving ground vehicles, all executed with minimal collateral damage to civilian centers. Remotely viewed damage assessments are also desirable for collateral damage verification. Precision-guided nonlethal weapons are also playing increasing roles in foreign affairs where international opinion is considered. With growing trends toward civilization infrastructure rebuilding in remote areas, foreign diplomatic missions need highly accurate means of delivering human aid and materials to depressed friendlies in remote populations centers, without inadvertently aiding enemy units. With the prospects of precision global positioning systems (GPS), airborne unmanned vehicular systems and methods are needed to provide accurate geolocating and targeting of both civilian and military ground targets.
A seeker with homing guidance can be used to achieve one foot or less miss distance accuracy required to enable a miniature bomb to be an effective precision-strike weapon released from a stand-off distance. Such seekers may require risky proximal release from a mother vehicle. Relative GPS navigation using pseudo star navigation can provide ten foot accuracy using simple seekers released from a low flying unmanned vehicle for providing a shorter range to target without risk to an overflying reference manned vehicle. Miniature precision guided bombs dropped from unmanned vehicles could harass and disrupt enemy movements and operation over wide areas without risks to pilots and with reduced risk to civilian centers. However, a maneuvering payload using conventional GPS navigation can not achieve a miss distance that is sufficiently accurate for miniature bombs. Miniature precision-guided weapons have a maneuvering radius that is determined by the acquisition range above a target and the lateral acceleration capability of the seekers. The field of view of the seeker is a limiting factor at very short acquisition ranges in the presence of high lateral acceleration capability. The cost of a smart seeker is proportional to the square of the acquisition range times the area of the field of view at the time of target acquisition. The size of the optical system and associated image stabilization systems is proportional to the square of the range where the computational complexity of target recognition depends on ambiguities in determining the target point, and this computation complexity is proportional to the area of the field of view. That is, the more precise the initial geolocation of the target by a target acquisition sensor, the shorter the required acquisition range and the smaller the area of the field of view. Reducing the target geolocation error and hence the required maneuver radius significantly reduces the seeker complexity. Conventional seekers with associated guidance processors have expensive precision optical components for guidance control for reducing the target geolocation errors that can presently resolve fine features such as windshields or exhaust pipes of moving vehicles. Hence, present geolocating and targeting systems do not provide inexpensive yet highly accurate homing seekers. These and other disadvantages are solved or reduced using the invention.
An object of the invention is to provide a method for locating a target.
Another object of the invention is to provide a method for locating a target using relative GPS navigation.
Yet another object of the invention is to provide a method for locating a target using relative GPS navigation for delivering a payload to the target.
A further object of the invention is to provide a method for locating a target using relative GPS navigation between a high altitude beacon platform transmitting a beacon, and a low altitude sensor platform for imaging the beacon using a beacon sensor, and for imaging the target using a target sensor.
Yet a further object of the invention is to provide a method for locating a target using relative GPS navigation between a high altitude beacon platform communicating a beacon, and a low altitude sensor platform for imaging the beacon using a beacon sensor having a beacon field of view, and for imaging the target using a target sensor having a target field of view both of which field of views have a common aligned boresight.
The invention is directed to a method for relative GPS navigation and targeting. Using a precise GPS relative positioning method, a beacon from an overflying aircraft can be used to reference boresight pointing angles of low altitude airborne sensors for significantly improving the geolocation accuracy of the target relative to low altitude sensor platforms. The high altitude vehicle is a beacon platform for providing the beacon as a reference. The low altitude vehicle is a sensor platform for imaging the beacon and for imaging the target. The beacon sensor and target sensor preferably have common aligned boresights for accurate imaging of the beacon relative to the target. The beacon platform and sensor platform use the same four GPS satellites for respective GPS position determinations. Both the beacon platform position and sensor platform position have approximately the same GPS positioning errors that cancel out in the relative GPS navigation solution, so that the relative GPS positioning error between two GPS navigation solutions is small. As such, precise offsets provided by relative GPS navigation provides highly accurate targeting. The sensor platform can determine the relative GPS location and precise target location for accurately guiding a maneuvering payload toward the target location.
The method improves the geolocation accuracy of airborne beacons that can be applied to the development of low-cost seekers for miniature precision-guided bombs, which can be carried by the low altitude sensor platform. The method reduces the target geolocation error for resolving aim-point ambiguities. The method can be used with seeker feature-recognition algorithms that can recognize distinct features, such as a windshield of a vehicle, and reduces the need for more complicated algorithms that must be able to select a particular vehicle among several similar vehicles. The geolocation method can also be used in other applications where improved boresighting accuracy is required and relative GPS navigation techniques can be employed. These and other advantages will become more apparent from the following detailed description of the preferred embodiment.